Lenses for sunglasses made from aromatic polycarbonate are produced by punching the functional sheet, which is comprised of a functional layer that has polarizability or photochromic ability or both, and the protective sheets attached to both sides of the functional layer, to form a shape of interest, curving it by using heat to form a partially spherical body, and injecting molten aromatic polycarbonate for lenses on a concave surface of the body. If necessary, the surfaces of the lenses obtained are subjected to finishing processes.
When the functional sheet is handled during commercial distribution, processing steps, etc., to protect the surfaces of the sheet from flaws, dirt, and contaminants, protective films are caused to adhere to the surfaces of the functional sheet. Specifically, polyolefin protective films were proposed. They are stable under a heat-curving process that uses high temperatures such as the glass transition temperature of an aromatic polycarbonate (Patent Documents 1 and 2).
Patent Document 1 discloses a protective film composed of two layers. One layer is a polyolefin film layer that has a substantive melting point of 150° C. or more. It is used as a surface layer. The other is a polyolefin film layer that has a substantive melting point of 125-145° C. and is used as an adhesive or gluing layer.
Patent Document 2 discloses a polyolefin film that is used as a protective film and is produced by coextrusion. The film has two melting peaks. One is 105-130° C.: (A) and the other is 160-175° C.: (B). The ratio of the areas of (A) to (B): [(A)/(B)] is 35/65-80/20.
Patent Documents 1 and 2 disclose the results of experiments to estimate the properties of products obtained by a heat-curving step (a heat-curving lens or product). However, they do not disclose any lens obtained by injection molding. Namely, they do not disclose any results of experiments to estimate the properties of products subjected to an injection molding process to produce a lens made by injection molding.
However, there is a problem that relates to a defect in the appearance of the injection molded lenses. Such a defect is seen as streaks that are white (white streaks). Such streaks are seen in a product after injection molding, i.e., an injection molded lens that is obtained by punching a functional sheet with the protective films to make the shape of interest, heat-curving to make a partially spherical product, attaching the product to an injection mold, and injecting aromatic polycarbonate on the concave surface of the product to make an injection molded lens. To increase the productivity of the injection molded lens, demands for the improved efficiency in the utilization of machines and for shortened times to produce such lenses are getting higher. But in complying with such demands, the increased frequency of white streaks was observed. This problem needs to be solved as soon as possible.